Free tropospheric BrO and the occurrence of ‘bromine explosion’ events that lead to the total depletion of surface ozone are intriguing, though not well understood, tropospheric BrO phenomena. Obtaining vertical resolution from ground-based total column measurements allows quantification of tropospheric BrO.

Differential Optical Absorption Spectroscopy (DOAS) UV-Vis measurements have been made for BrO at Arrival Heights, Antarctica (77.83S, 166.66E). Observations are made using three different viewing geometries and the measurement ensemble is used in this study to improve our understanding of the vertical distribution of BrO in the southern polar atmosphere. Direct-sun and off-axis measuring modes provide sensitivity to tropospheric absorbers while the complementary zenith-sky mode is sensitive to stratospheric absorbers.

Long term zenith-sky and off-axis observations of BrO have been made (since 1995 and 1999 respectively) and these combined with a short campaign of direct-sun measurements in spring 2002 provide a comprehensive measurement study of BrO at this southern hemispheric polar site. A radiative transfer model is coupled with a formal optimal estimation retrieval algorithm to retrieve stratospheric and tropospheric columns for BrO. An investigative study of the measurements is performed to evaluate their information content and errors. This data set will be investigated using ancillary data, such as in-situ ozone measurements and ozonesonde profiles, pressure, visibility, wind speed and direction.